I just reviewed a recent Continental Service Bulletin on the S-20, S-200 and other mags discussing a loose bushing that can account for damaging distributor gears. Following is the first couple paragraphs, and a link to Continental SBs:
CONTINENTAL MOTORS® IGNITION SYSTEMS SERVICE BULLETIN Compliance Will Enhance Safety SUBJECT: Continental Motors S-20, S-200, and S-1200 Series Magneto Distributor Gear Block Inspection PURPOSE: Inspect magneto distributor block to determine condition of magneto's distributor gear bushing. COMPLIANCE: During the next 100-hour, progressive, or annual inspection, whichever occurs first and every 100-hour, progressive or annual inspection thereafter not to exceed the applicable time in service requirement. MODELS AFFECTED: All aviation gasoline engines utilizing Continental Motors, Inc. (formerly TCM/Bendix) S-20, S-200, and S-1200 Series Magnetos I. General Information Magnetos manufactured by Continental Motors, Inc. (CMI) contain a bronze oilite distributor gear bushing in the distributor block that supports the distributor gear shaft. The distributor gear bushing is bonded to the distributor block during its manufacture. CMI is aware of instances in which the distributor gear bushing has become loosened in the distributor gear block. The loose bushing may result in an offset or disengaged distributor gear, damaged distributor gear teeth, and/or rough running engine operations. As a result, this service bulletin specifies an inspection procedure to determine if the distributor gear bushing has become unbonded from the distributor block. NOTE: This service bulletin is not intended to replace the recommended periodic maintenance intervals and magneto maintenance procedures as outlined in the published CMI Magneto Service Support Manuals Here is the link: http://continentalmotors.aero/Support_Materials/Publications/Service_Bulletin_Search/ On Wed, Oct 7, 2015 at 4:43 AM, Ian Mc Phee <[email protected]> wrote: > That is good to hear your (Nigel) explaination re Stemme and it's extra > demands on a magneto. > > Ian m > On 7 Oct 2015 1:07 pm, "Nigel Baker" <[email protected]> wrote: > >> The gears are not under much load when running I agree. >> However when the impulse coupling is in action the acceleration loads >> must be considered and this is considered the cause of failure. >> The Stemme is unusual in that you have to run the engine on the starter >> till the blades are deployed then go for the ignition so they go though >> points faster than we do for that reason and it is also harder on the gears >> than our aircraft are. They also suffer impulse coupling (ware) failures >> more than we do due to the more time running on them. >> Cheers. >> Nige. >> >> >> *From:* Rob Thompson <[email protected]> >> *Sent:* Monday, October 05, 2015 8:47 AM >> *To:* [email protected] >> *Subject:* RE: [DOG mailing list] Mag Failure >> >> I think I might direct a 25mm air hose through the baffle straight onto >> the magneto. We have our motor very well sealed with silicon and running >> cool so I think we can spare that amount of air. >> >> Each Rotax ignition generates 2 sparks, once when the flywheel magnet >> hits the coil, second when the trailing edge of the magnet passes the coil. >> The sparks are reverse polarity. >> >> At startup with weak sparks, a zener diode will block the normal slightly >> advanced spark. This is a very unreliable way of doing it and doesn't alway >> work that well. Kick backs are the worst of the problems when the Zener >> doesn't block the advanced spark properly. >> >> Starting on one only ignition circuit will help the problem but I have a >> soft start circuit diagram that your Foxbat friends might be interested in. >> >> Rob Thompson >> 0429 493828 >> *Please note that my new email address is [email protected] >> <[email protected]>* >> >> >> ------------------------------ >> From: [email protected] >> To: [email protected] >> Date: Mon, 5 Oct 2015 10:24:31 +1300 >> Subject: RE: [DOG mailing list] Mag Failure >> >> A couple of points of interest, >> >> 1) I have been doing some delivery flying and test flying of a few >> Foxbat microlites which have the 100hp Rotax 912 engine. They have >> electronic ignition. On start up, the engine runs like a hairy dog for a >> few seconds then smooth … as the electronic pick ups are changed >> automatically from the TDC start ones to the normal advance ones … maybe >> a similar idea could be designed for a limbach pickup(s) >> >> 2) We have also had a mag failure on a Grob 109 … quite a few years >> ago though. Could it be that the 109 mag cooling is simply not up to >> scratch ?? Wolf Hoffman seems to have cunningly used the cooling airflow >> thru oil cooler to be directed over the mag of the Dimona. While warm >> air of course, it still seems to offer significant cooling >> >> Ian Williams >> >> ZK-GCB >> >> >> >> *From:* [email protected] [mailto:[email protected]] *On >> Behalf Of *Rob Thompson >> *Sent:* Saturday, 3 October 2015 11:08 a.m. >> *To:* [email protected] >> *Subject:* RE: [DOG mailing list] Mag Failure >> >> >> >> Those gear teeth don't drive much of a load except if the rotor was to >> jam for some reason? >> >> Not easy to tell from the photo but the rotor gear teeth look OK. Maybe >> if heat is a factor the stripped gear may use plastic that softens at a >> lower temperature. >> >> Did this happen at start up? If so the gear teeth undergo some serious >> acceleration as the impulse coupling kicks. >> >> What about at shutdown? If the engine kicks back the gear teeth also >> reverse direction suddenly. >> >> Some serious analysis needed...I guess all will be revealed in time! >> >> Rob >> >> Rob Thompson >> 0429 493828 >> *Please note that my new email address is [email protected] >> <[email protected]>* >> >> ------------------------------ >> >> From: [email protected] >> Date: Sat, 3 Oct 2015 10:33:42 +1300 >> To: [email protected] >> Subject: Re: [DOG mailing list] Mag Failure >> >> Could well be temperature related >> >> Sent from my iPhone >> >> >> On 3/10/2015, at 08:46, Ian Mc Phee <[email protected]> wrote: >> >> My question is why does it happen? Is it based on hours or cycles of >> starts or getting too hot or something else. I can remember once at >> overhaul he replaced the cog gear as it looked a little damaged >> >> Ian m >> >> On 3 Oct 2015 12:15 am, "Nigel Baker" <[email protected]> wrote: >> >> Attached image of what failed in Rob’s Maggy. >> >> The drive gear stripped/lost a tooth and took the distributor gear with >> it. >> >> Cheers. >> >> Nige. >> >> >> >> >> >> --------------------------------------------------------------------- >> You are subscribed to the Dimona Owners Group mailing list. >> To unsubscribe, send email to: [email protected] >> >>
